The present invention relates to shoes suitable for horses, or any animal requiring hoof protection, prepared from ultra-high molecular weight polyethylene.
One of the major causes of lameness in horses is the direct result of horseshoes that restrict the natural flexing (i.e. expansion and contraction) of the horse's foot, maximize concussion, cause corns, enhance fatigue from their heavy weight, inflict severe cuts and bruises, and provide inadequate protection. Whether used for pleasure, work, or competition, horses are used on a wide variety of surfaces, natural and artificial, which can cause overstressing and damage tendons, cartilage, and bone. It has been suggested that fatigue failure is a major cause of lameness, and lameness is directly related to the hardness of the surface on which horses are used.sup.1. Data show a linear, direct relationship between lameness on California racetracks and the hardness of the tracks. The peak shock level on a horse's hoof is about 2000 pounds of force when galloping across pavement or hard dirt, and 800-1000 pounds on grass. This shock can be greatly reduced by using a shoe that has good shock resistant and impact resistant properties. When shock and concussion are reduced on the horse's feet and legs, lameness is reduced. FNT .sup.1 "Foreleg Fatigue Fracture," Cheney, J. A.; Lion, S. Y.; Shen, C. K.; Wheat, J. D., Thoroughbread of California, November 1971.
With the increasing number of pleasure horses, work horses (metropolitan mounted police), and draft horses being used on paved surfaces, there is concern being given to the damage hard metal shoes cause to the surfaces. Indeed, several articles have been written expressing this concern and the subsequent increased costs of street and road maintenance and repair. Horse owners, including trail riders, Amish draft horse owners, and municipalities, are encouraged to replace hard metal shoes with more resilient, less damaging shoes. Similarly, the destruction and enhanced wear on private barn floors, walkways, and surfaced paths resulting from hard metal horseshoes is significant.
Another concern to the horse owner that results from the use of hard metal shoes is the restricted "natural" action of the hoof. When a horse is in motion, the natural movement of the hoof is to expand slightly under weight and to contract when the animal's weight is shifted. Rigid metal shoes restrict this natural hoof action, which further contributes to fatigue and lameness..sup.2 A further disadvantage to the use of hard, rigid shoes can be found in that, when this natural hoof flexing is restricted by the shoe, there is a tendency to place considerable stress on the nails holding the rigid shoe to the hoof that normally expands and contracts, resulting in the loosening of the nails or pulling the nails through the hoof and eventually throwing the shoe. A heavy, hard metal shoe that comes loose or is thrown can inflict severe cuts or bruises to the animal. FNT .sup.2 The complex action of the parts of the hoof has been described in several articles in the literature. A comprehensive study of the structure and behavior of horses' feet in action may be found in the August 1977 issue of Saddle Action, published by Saddle Action, Inc., Paso Robles, Calif., pages 18-21, 50, written by K. D. Butler, Jr.
Accordingly, there exists a need for a light weight, shock absorbant, abrasion resistant, flexible horseshoe that will provide therapeutic advantages to the animal and minimize damage to the surfaces on which the animal is used.
Many attempts have been made in prior art to provide a protective device for the horse's foot incorporating the objectives mentioned above. For example, the hoof coverings described in U.S. Pat. Nos. 4,235,292 and 4,206,811 consist of an integrally designed steel yoke in a plastic body attached with screws. U.S. Pat. Nos. 4,189,004; 3,703,209; and 3,732,929 teach that polyurethane rubber boot-type horseshoes have desirable characteristics. A hard rubber sheet containing small metal fragments is described in U.S. Pat. No. 3,513,915. Indeed, cast polyurethane horseshoes appear to be the preferred material for flexible horseshoes, as described in U.S. Pat. Nos. 3,494,422; 3,490,536; and 3,469,631. The types of shoes as described in these references overcome some, but not all of the recognized shortcomings of metal horseshoes.
An existing need remains for an economical, light weight horseshoe which will protect the horse's hooves and be simple to attach to and remove from the horse's hooves.